U.S. officials have told Reuters that the United States will send about 3,500 additional troops to Afghanistan.

Puerto Rico and the U.S. Virgin Islands were battered by hurricanes Irma and Maria. Hurricane Maria knocked out power to Puerto Rico's 3.4 million residents last month, devastating the island's already dilapidated electric power infrastructure.

There are about 11,000 U.S. troops assisting in relief efforts to Puerto Rico, along with a number of naval vessels, according to the Pentagon.

McKenzie added that relief efforts would also slow the deployment of the Wasp, an amphibious assault ship, to the Pacific at a time of heightened tension between North Korea and the United States.

Defense Secretary Jim Mattis said earlier this week that hurricane relief efforts could have an impact on troop deployments, but did not specifically mention Afghanistan.

"We are ready to go even to the point that it's going to impact the deployments, perhaps, of some of these troops overseas next year, because we've interrupted their preparation," Mattis told a Senate Armed Services Committee hearing.